Selective solvent extraction of petroleum



March 7, J Q, O ETAL SELECTIVE SOLVENT EXTRACTION PETROLEUM 2Sheets-Shet 1 Original Filed Aug. 17, 1937 my hw P538 F mm UQN .WMIJ MNA N \w 1 w ww mm L E ww M \W mm \m mm a? Q v mm mm 3 1: w m m w m LEZEEr m R. m w Q Mm QM O 0 m N\ N H. H. v 444. I w \JQ\ Q S 8 Q X1 59w233055 ma /V7025 JOH/V 060, 15

x U M C H M M W March 7, 1944. J. Q. COPE EI'AL SELECTIVE SOLVENTEXTRACTION PETROLEUM ori inal Filed Aug. 17, 1937 2 Sheets-Sheet 2lnvenfor: JOHN Q. COPE 'W/LL/AM HCZA USJSf/V xuokm Patented Mar. 7,1944- SELECTIVE SOLVENT EXTRACTION F PETROLEUM John Q. Cope and WilliamH. Claussen, Berkeley, Calif., assignors to Standard Oil Company ofCalifornia, San Francisco, Calif., a corporation of Delaware Originalapplication August 1'7, 1937, Serial No.

159,522. Divided and this application September23, 1940, Serial No.357,892

9 Claims.

This invention relates to a process of refining petroleum with aselective solvent. More particularly, it involves a process of treatingnormally liquid petroleum hydrocarbons in vapor phase with a liquidphase selective solvent to effect a more efficient separation of thehydrocarbon components into fractions of different chemical types.

As is well known, normally liquid petroleum contains a complex mixtureof hydrocarbons of different types. For example, certain naturalpetroleums are known to contain a minor percentage of aromatichydrocarbons and a major proportion of paraffins and/or naphtheneshaving five, six and seven carbon atoms in the naphthene ring. Becauseof close similarity in properties it has been very difficult to separatethese hydrocarbons according to their chemical types. Liquid phaseextraction of petroleum oils with selective solvents at temperaturessubstantially below the point at which the solvent is completelymiscible with the oils, constitutes one known method of refiningpetroleum and separating aromatic and/or naphthenic hydrocarbons fromthe remaining oil. Although such a process produces an extractcontaining relatively more aromatic and/or naphthenic hydrocarbons and arailinate relatively more paraffinic in nature, the separation is onlyqualitative and yields fractions containing substantial quantities ofhydrocarbons which it was desired to eliminate.

It is a well accepted general rule in the art of selective solventrefining that an increase in the temperature of extraction, although itincreases the yield of extract obtained, decreases the selectivity of agiven solvent and yields an extract in which the separation betweenaromatics and/or naphthenes on the one hand and paraffins on the otherhand is less sharpi'than obtained at lower temperatures. That is. astemperature of extraction is increased, the yield of raffinate islowered and the extract contains more and more of the hydrocarbons whichit is desired to keep in the raiflnate. When the temperature ofextraction is lowered, the yield of railinate increases but it containsan increased amount of the type of hydrocarbons (e. g. aromatic and/ornaphthenic) which it is desired to retain in the extract. Accordingly,it has heretofore been regarded as necessary to adopt temperatureintermediate the above mentioned high and low extremes such that a givensolvent will yield a satisfactory quantity of rafiinate and yet alsogive a reasonably efficient separation or refinement of the petroleumoils.

We have d scovered that by increasing the temperature of extraction tothe boiling point of the hydrocarbons being extracted, a remarkable andunpredictable reversal in the efiectiveness and selectivity of thesolvent extraction process is produced.

Accordingly, an object of the present invention is to provide a simple,effective and improved p-rocess of refining petroleum with a selectivesolvent.

Another object is to provide a process of refining petroleum With aselective solvent by countercurrently contacting a normally liquidpetroleum fraction with a liquid phase selective solvent having apreferential solvent action for one class of carbon compounds such asaromatics, at a temperature no lower than the initial boiling point ofsaid petroleum fraction under the conditions of extraction andpreferably no lower than the dew point of the petroleum fraction.

A further object is to provide a single multistage extraction processfor continuously sepa rating petroleum into a plurality of separateportions comprising a fraction highly aromatic in character, a fractioncontaining a high content of the sulfur bodies present in the petroleum,a fraction highly naphthenic in character and a fraction consisting ofhighly parafimic compounds.

Another object is to provide a process of selective solvent extractioncapable of effecting substantially quantitative separation of aromaticand/or naphthenic hydrocarbons from a normally liquid fraction ofnatural petroleum containing paraffinic compounds having boiling pointsas much as 20 to F. higher than the lowest boiling aromatic compoundpresent.

An additional object of the invention is to provide a process capable ofeirecting quantitative separation of aromatics from a fraction ofnatural petroleum containing a minor proportion of hydrocarbons of thearomatic type.

A further object of the invention is to provide improved selectivesolvents for extraction of petroleum.

In the drawings,

Fig. 1 is a diagrammatic flow sheet illustrating a multi-stage vaporphase selective solvent extraction process embodying the principles ofthis invention.

Fig. 2 is a diagrammatic illustration of a process utilizing a singlestage vapor phase contacting tower for carrying out the selectivesolvent extraction process of this invention.

Briefly, the process of this invention involves countercurrentlycontacting normally liquid petroleum hydrocarbons with a higher boilingselective solvent maintained in liquid phase and at a temperature abovethe boiling point of the hydrocarbons being treated. By this processaromatic hydrocarbons, or when desired naphthenic hydrocarbons, or both,are selectively ex tracted from the mixed vapor phase petroleumhydrocarbons.

In the process as illustrated by the flow sheet of Fig. l, the petroleumstock to be treated is passed from storage through pipe I, heatexchangers 2 and 3, and conduit 4 to the vaporizer 5. The petroleum isconverted from liquid to vapor phase in the vaporizer 5 and then passesthrough line 6 and valve l2 to extracting column 1.

To insure intimate contacting in the extraction column between the vaporphase petroleum and the liquid phase selective solvent, various meansmay be adopted. A tower filled with suitable packing of refractoryearthenware, glass, etc., comprises one efiective form of apparatus forthis purpose. A tower constructed in the same manner as an ordinaryfractionating column of a bubble cap type is also an efficient means ofinsuring effective contact between the vapor phase petroleum and theliquid phase extracting solvent. In Fig. 1, three extraction columns areshown but it is apparent that the number may be increased or decreasedas conditions such as efliciency of the extraction, the volume ofmaterials to be treated, etc., require.

After extraction in tower I the rafiinate vapors pass from the top ofthe tower through line 8 to the bottom of extraction tower 9. Theraffinate from extraction tower 9 likewise passes through line l totower II where the raffinate hydrocarbons, still in vapor phase, areagain extracted by the selective solvent. The final vapor phaseraffinate flows from the top of extraction tower ll through conduit l4and control valve l to heat exchanger 2 where partial condensationoccurs. Provision is made for returning a por tion or all of the partialcondensate from heat exchanger 2 through valve controlled line Hi toeither extraction tower 9 or I I or both by means of independent returnpipes controlled by valves l1 and I8 therein. The remaining raflinate iscooled in condenser l9, condensed to liquid phase and passed to storage.Valve controlled conduit ISA provides means for supplying additionalcondensate for reflux when the desired reflux ratio is higher than thatobtainable by using the partial condensate alone.

The selective solvent which has been referred to in the previousparagraphs, flows through extraction columns I, 9 and H countercurrentlyto the vapor phase petroleum being extracted. Fresh solvent is admittedto the top of tower II through inlet line 20 controlled by valve 20A.The solvent flows down through thecolumn and extracts those hydrocarbonsfor which it has a selective action from the upwardly flowing vaporphase petroleum. The solvent with the selectively dissolved petroleumvapors is continuously removed from the bottom of the column throughline 2| to vaporizer 22. To obtain more efficient extraction it isdesirable to heat the solvent in a vaporizer such as 22 in order tovaporize a substantial proportion of the dissolved hydrocarbons andrecirculate these vapors to the extraction column. This procedure tendsto eliminate hydrocarbons of the raifinate type which have condensed orwhich have been dissolved in the solvent. Also, the recirculation ofthese vapors provides a method of adding heat to tower I l.

The solvent, after being heated in vaporizer 22. flows through line 23into the top of extraction tower 9. The solvent then countercurrentlyextracts petroleum vapors in tower 9 and flows through line 25, heater28 and line 2'1 to the top of tower 1 in the same manner as in thepreviously described extraction step. From the bottom of extractiontower I the solvent together with the dissolved hydrocarbons is removedthrough line 3| to vaporizer 32 where a small portion of the dissolvedhydrocarbons is vaporized and returned to the extraction tower I throughline 33. The selective solvent and extract then flow from the vaporizer32 through valve 34 and line 35 to fractionating still 36. The extractedhydrocarbons are separated from the selective solvent by distillationand are removed from the top of the fractionating column through line31, passed through heat exchanger 3 and condenser 38 to storage.

The solvent is continuously recirculated from still 36 through line 20to the extracting system as previously described. New or additionalsolvent can be supplied to the system as needed through valve controlledline 39 from the solvent storage tanks. It is to be noted at this pointthat the solvent entering the extraction system from the still 36 isheated to a temperature above the boiling point of both the extract andraffinate. The temperature of the solvent in the extraction towers mustof course be maintained below that at which a major proportion of theextract would be vaporized from or remain undissolved in the solventwhile being extracted. This temperature is, however, above the normaldew point of the extract as well as of the raffinate hydrocarbons at thepressures existing in the system.

An auxiliary line 28 leading from vaporizer 5 and a control valve 49 areprovided so that the petroleum vapors may be introduced into extractiontower 9 rather than into extraction tower I. When the vapors are sointroduced, control valve 40 will be open and valve l2 in vapor line 6will be closed. It is also apparent that the incoming hydrocarbon vaporsmay be introduced in both towers T and 9 by opening both valves 49 andI2.

Under various conditions it is desirable to remove side streams or cutsfrom the extracts of the different stages of extraction. Accordingly,valve controlled conduits 4| and 42 have been provided for this purposeand permit the removal of extract cuts from extractors 9 and IIrespectively. The portions of extract removed through these conduitswill be separately distilled in a fractionating still similar to 36shown in Figure 1 to separate the extracted compounds from the solvent.These additional stills have been omitted from the flow sheet for thesake of simplicity.

By controlling the conditions of extraction in the various stages it ispossible to obtain an extract from treater I which is substantially freefrom sulfur compounds and which is predominantly or entirely aromatic inchemical constitution. Likewise, by proper control an extract cut fromtreater 9 which contains a high proportion of sulfur bodies present inthe petroleum and an extract cut from treater l I which is predominantlynaphthenic in character may be obtained. In order to obtain theseresults it is of course necessary to maintain the temperature in treater1 above the boiling point of the sulfur bodies, naphthenic compounds andparaffinic compounds in the petroleum, but within the range at whicharomatic compounds are preferentially extracted by the selectivesolvent. In a similar manner the temperature in extractor 9 will beabove the boiling point of the naphthenes and paraliins, but within therange at which sulfur compounds are preferentially dissolved by theselective solvent. In treater II the temperature will be sufficientlyhigh to cause vaporization of the paraflinic compounds and yet withinthe range at which naphthenes will be extracted by the selectivesolvent. Obviously, the specific temperatures, pressures andsolvent-to-oil ratio necessary to produce these results will vary withthe selective solvent being used and with the petroleum stock beingtreated. With a given solvent and a given stock the proper conditionscan be readily determined by experiment.

In view of the above discussion it is apparent that by the processrepresented in the flow sheet of Fig. 1 a petroleum fraction can becontinuously separated into four separate fractions of distinctlydifferent chemical constitution by passing the petroleum fractionthrough a series of three or more extraction Zones, passing a liquidphase selective solvent through each of said extraction zones,intimately contacting the petroleum and the selective solvent in saidextracting zones, maintaining said selective solvent in each of thezones at a temperature no lower than the boiling point of the petroleumfraction under the conditions of extraction in that zone, maintainingthe temperature of the solvent above the boiling point of thenon-aromatic compounds in the first zone of extraction but below thepoint at which all aromatic compounds would be vaporized from thesolvent, maintaining the temperature of the solvent in the secondextracting zone above the boiling point of the parafiinic and naphtheniccompounds but below the point at which all sulfur bodies would bevaporized from the selective solvent and maintaining the temperature ofthe solvent in a third extraction zone above the boiling point of theparafiinic compounds, but within the range at which substantially allthe cyclic non-benzenoid compounds are selectively dissolved. Theparafiinic compounds will then be removed in vapor phase from the thirdextraction zone and aromatics, sulfur bodies and naphthene compounds inthe extracts from extraction zones 1, 2 and 3, respectively.

An added refinement which may be utilized in the process illustrated byFig. 1 comprises operating extraction towers l, 9 and l at successivelydecreased temperatures and pressures. In this species of operationextractor 1 will be maintained at substantially atmospheric pressures,for example, extractor 9 at an intermediate reduced pressure andextractor l I at the lowest pressure and highest vacuum. Vacuum can beproduced by the use of condenser I9 and pump 45 or by other suitable andwell-known arrangements of apparatus. Throttle valves 43 and 44 in vaporlines 8 and I respectively are utilized to efiect a pressuredifferential between extractors 9 and II. Pumps 46 and 41 in lines 2'!and 23 serve to feed the solvent from the zones of lower pressure to thezones of successively higher pressures. Pump 48 is provided in thereflux line to extractor 9 to feed the reflux from line It to extractor9. This pump is necessary when as in the case of the present species ofoperation extractor 9 is operated at higher pressures than extractor II.

By utilizing successively higher vacuum, that is successively reducedvapor pressures in the successive stages of extraction, improvedseparation of aromatics from parafiins and greater eificiency ofoperation may be obtained.

The flow sheet of Fig. 2 illustrates an alternative simple but veryefiective methodfor operating the process of this invention. In thisarrangement petroleum stock to be treated passes from storage throughvalve controlled line 50, heat exchanger 5l, line 52, heat exchanger 53,line 54, vaporizer 55, and line 56 to a single extraction tower 51. Theliquid phase selective solvent together with its dissolved extract fiowsfrom the bottom of tower 51 through line 58 to vaporizer 59. A portiononly of the extract is flashed into vapor form and re-circulated throughline- 60 to tower 57. Solvent is continuously removed from vaporizer 59through line BI and passed to still 62 for removal of the extractedhydrocarbons. The extract is separated from the solvent in fractionatingcolumn 63 and flows through line 64, heat exchanger 53, line 65 andcondenser 66 to stor age. The selective solvent is continuously removedfrom the still and re-circ'ulated to extraction tower 51 through valvecontrolled line 61. The liquid level in the Vaporizers 55, 59 and 62 ismaintained above the conduit connections 54, 53, 6i and 61 to produce aliquid seal and prevent the flow of vapors through these conduits.

Rafiinate vapors flow from the top of extraction tower 51 through line68 to'heat exchanger 5| where partial condensation occurs. As much ofthis partial condensate as is desired may be returned to the extractiontower through line 10 controlled by valve TI. The remainder of thereflinate passes through condenser 69 to storage. Valve controlledconduit I2 provides means for supplying additional condensate to thereflux line when the desired reflux ratio is higher than that obtainablewith the partial condensate alone.

In a single stage extraction process it is essential that the vaporphase hydrocarbons and liquid phase solvent be intimately contacted. Oneefficient means for effecting this result comprises the conventionalbubble cap fractionatin column in which the vapors to be extracted riseupwardly through a series of bubble caps and are thereby intimatelymixed with the downflowing extracting solvent. Such an extraction toweris the preferred form utilized in the process of both Figs. 1 and 2.

To illustrate the characteristics of the process the following data aregiven.

A natural petroleum out having a boiling range of 200 to 300 F. wasextracted in a single bubb le cap tower with an arrangement of apparatussimilar to that illustrated diagrammatically in Fig. 2. The dataof atypical run using crude xylenols which had been topped at 450 F., as theselective solvent are given below:

Rate of petroleum feed cc./mi'n 5 Rate of solvent feed cc./min 25Temperature at base of extraction column F 288 Temperature of rairlnatevapor -F 216 Temperature of still F 490 Temperature of extract vaporfrom strippin colulllinw- F' 249 Tem erature of solvent enteringextraction communa -i F' 254 Temperature of stock entering column F 245Reflux ratio of rafiinate 1.9 Extract yields.-. -e per' cent" 38 Anilinepoint of stock fed -JFL; 44.4 Aniline point or raninate F Aniline pointor extract F 15 In this run the temperatures of feed and solartivesolvent were 5 to and 10 to 20, respectively, above the dew point ofthe stock.

-A series of tests was run to determine the effect of reflux of theraffinate on the aniline point spread and yield of extract. Two seriesof data were obtained, one for a solvent thinner ratio of five to one,and one for a ratio of one to one. The extract yield was held constantto 40% and the other variables, such as temperature, as close to thosevalues given above as possible. The reflux ratio was varied during thesetests to determine the effects on the aniline points of the rafiinateand extract. It was found that the optimum reflux ratio is zero. At thatratio the aniline point of the extract is as low as can be obtained withthat particular extract yield and solvent stock ratio. The lower theyield, of course, the lower the aniline point of the extract.

When the optimum reflux ratio of zero is used, itwas found that theoptimum ratio of solvent to petroleum was approximately three to one.Increased ratios up to as high as five to one give appreciable benefitsin the extraction process. The increased efl'iciency of extraction whichresults from solvent ratios above five to one is relatively small.

In an arrangement of apparatus such as shown in Fig. 2 where the still62 is separated fromthe extraction column by liquid seals so thatextract vapors cannot return to the extraction column. it was found thatthe optimum rafiinate to re flux ratio was approximately 2:1.

volved and that the less volatile rafilnate hydrocarbons having aboiling point 20 to 60 higher than that of the extract hydrocarbonswould be almost quantitatively separated as a vapor phase.

There is, of course, a practical limit to the range of boiling pointspread between the extract and rafiinate hydrocarbons which ispermissible if pure aromatics are to be obtained by selective solventextraction in the vapor phase. When paraffinic and aromatic hydrocarbonsare being separated, those paraflinic hydrocarbons having a boilingpoint more than 100 F. above the boiling point of the aromatics aredissolved in the solvent and will be removed with the extract in a vaporphase extraction process. Paraffine hydrocarbons having boiling points20 to 60 F. above the boiling point of the aromatics being extractedcan, on the other hand, be eiIectively separated as raffinate vapors.Parafiine hydrocarbons having boiling points equal to or lower than thearomatics being extracted present no difliculty whatever since they arereadily separated in the vapor phase. In other words, when theparafiinic and naphthenic compounds present in the petroleum out haveboiling points no more than 60 F. above the lowest boiling aromaticwhich is extracted, an extract free from these higher boiling compoundscan be produced.

Table No. 1 illustrates results obtained with different solvents intreatments on different types of petroleum oils.

Table No. 1

- Extract Rafllnate Solvent to Raflinate Solvent l Natural petroleumstock treated g g? g a aniline aniline stock reflux l p y point pointratio ratio F. Percent F. F.

Phenol 200-300 F. cut California crude 44. 3 -44.4 116. 2 5. 6 1 D0-.- d44.3 18 --75.4 81.8 5.6 1 D0 d0 44.3 20.4 114.4 5.6 1

Crude xylenol topped to 450 F. 300400 F. cut California crude 42. 5 19+11. 6 44 5 1 Do soc-350 F. cut California crude 30. 4 26 -15. 2 47. 6 51 Do 200-300 F. cut California crude. 44. 4 40 -27 76 5 0 'lriethyleneglycol ..d0 44. 4 39 40. 4 102. 8 5 0. 0 D0 H 44. 4 30 -30. s 95. 4 5. o1 1. 9

I All aniline points were determined by the equal volume method or bytefractive index. 1 Apparatus provided with liquid seal betweenextraction and extract stripper columns.

It has also been found that with various selective solvents, such asxylenol, the extraction process is selective with respect to raflinatehydrocarbons having a boiling point as much as 60 F. above the boilingpoint of the aromatic hydrocarbons being extracted. In ordinaryselective solvent liquid phase extraction processes, selectivitydecreases with increase in temperatures. At temperatures of 400 to 500F., such as are involved in the process of this invention, selectivesolvents have heretofore been regarded as entirely ineffective sincethey dissolve the millnate hydrocarbons practically as readily as theextract hydrocarbons obtained at lower temperatures. Also, it is agenerally accepted principle that as between two solutes dissolved in agiven solvent, the higher the boiling point of a given solute the lessis its tendency to vaporize from the solution. That is, the lowestboiling dissolved hydrocarbon components should most readily vaporizefrom the solvent and the higher boiling hydrocarbons (such as therafiinate hydrocarbons boiling 60 above the extract hydrocarbons in thepresent process) should tend to dissolve and remain in solution.Certainly it is not obvious that the much more volatile constituentswould be selectively dissolved at the high temperatures in- A selectivesolvent useful for the present process should be highly selective andshould have a boiling point well above the end point of the stock to betreated. A boiling point above approximately 300 F. will generally befound desirable for extraction of normally liquid low boilinghydrocarbons. Preferably the solvent should not form constant boilingmixtures with hydrocarbons, but if such constant boiling point mixturesare formed, the solubility characteristics of the solvent should be suchthat complete recovery by water extraction is possible. Constant boilingmixtures of the solvent with water should not be formed or additionalcomplications will result from the use of water in solvent recovery.Various solvents with the above desired properties have been found andare listed in Table No. 2.

In order to test the relative selectivity of S01- vents a simplecomparative test was adopted. This test consisted of adding a petroleumout having a boiling point of from 215 to 240 F; to cc. of the solvent.The petroleum was added slowly and with constant stirring so that thesolvent could be maintained at 250 )5. during the test. A portion of thedissolved petroleum was vaporized from'the mixture at this temperatureand the first 3 cc. of overhead were taken for an aniline point test.The elevation of this aniline point over that of the original stock isdesignated selectivity.

Table No. 2 lists the solvents tested in the order of their selectivityas determined by this method. Solvents having a selectivity factorgreater than 25 are operative in the vapor phase extraction process ofthis invention providing they also have a boiling, point substantiallyabove the dew point of the hydrocarbon fraction being extracted.Attention is directed to the fact that this test merely indicates therelative selectivity of the solvents and that much greater aniline pointspreads are obtained by the actual process of this invention. Forexample, xylenol has a selectivity of 32.1 as deterrm'ned by the testbut gave an aniline point spread of 103 F. between the extract andraflinate when used to treat a 200 to 300 F. boiling point petroleum out(see Table 1).

Table No. 2

Selec- Solu- 4 Solvent V. P. I. tivity bimy 1 529 60. 2 35 349 at 40 mm.(30 40 293 at 0.1 mm 56 30 360 55. 1 80 55 26 54. 3 48 51. 3 80 51.1 2050. 53 49. 8 22 47. 7 90 46. 3 74 45. 8 80 43. 9 15 42. 8 170 42. 4 140Ohlorex 39. 7 166 Diaminopropanol 39. 7 15 Tricresylphosphate 38; 9 95Benzaldehyde... 35a 38. 2 162 Triethanolamine 36. Eugenol 36.- 4 9eDiphenylamine 34. 6 185 Acetophenone 34. 4 150 euol 32. l 140 Carbitolacetate 32. l 168 Butyl carbitol. 29. 9 130 Phenetidlne 29. 5 205Dibutyl phthalate 27. 6 140 1 Number of cc. of 215-240 F. straight runpetroleum cut dissolved by 150 cc. of solvent at 250 F. and oneatmosphere total absolute pressure.

Tetraethylene glycol and triethylene glycol have selectivity factors of56.7 and 55 respectively. These solvents also have very high boilingpoints and are highly eflicient selective solvents for vapor phaseextraction.

Triethylene glycol is a preferred selective solvent for the presentprocess. It has a very high selectivity, is stable, non-corrosive andhas thevery high boiling point of 550 F. The high selectivity of thiscompound is illustrated by a runin which a petroleum stock having aboiling point range of from 200 to 300 F. was treated and an extractproduced having an aniline point of 40 F. The spread of aniline pointbetween the rafiinate and the extract was 143.? as compared with 103with xylenol under the same conditions. Even with. a 300 to 400 F.boiling. range. petroleum out which necessitated. extraction atmuchhigher. temperatures than with the 200 to. 300 F. cut, a. -2 l F.aniline, extract was produced. andatotal spread of aniline point betweenraifinate and extract of 104.2" obtained.

In a six. hour test at. 550 F., the maximum decomposition of the;triethylene glycol was a. change of 0.1% determined from boiling pointcurves taken before and after the test. Other. tests failed to showanydecomposition. of, the

triethylene glycol. The maximum corrosion observed on iron or steel was0.008 inch per year at 550 F.

In a long run using the type of apparatus illustrated by Fig. 2, it wasfound that a small amount of triethylene glycol distilled over with theextract and raffinatefractions. The amount of triethylene glycoldissolved inthe extract portion of the hydrocarbons was of the order of0.15% by volume. This small amount of triethylene glycol is easily andcompletely removed by water washing and the solvent can then berecovered by the evaporation of the water therefrom.

A more advantageous method for recovering the solvent from the washwater is to' feed the water containing the solvent into the still andiractionating' column along with the extract layer. This method has theadvantage that it breaks up the constant boiling mixtures of solventsand high boiling extracts which may tend to form. The water andhydrocarbon extract come over as overhead and are readily separated. Inthose cases where there has beenincomplete removal of water from theselective solvent, the effect is merely to render the solvent moreselective in the extraction step of the process. That is, the anilinepoint of the extract is lower and the yield of aromatic hydrocarbonsdecreased.

As stated above, simple water washing completely removes even. veryminute amounts of triethylene glycol which may be dissolved in thepetroleum. For example, it has been found that when a 300 to 400 F. cutof petroleum is contacted with a water solution containing 20% by weightof triethylene glycol, no. detectable amount of triethylene glycol canbe found in the petroleum layer. These data indicatev that triethyleneglycol has a very high partition coefficient between petroleum and waterso that this solvent readily diffuses almost quantitatively from oil toWater.

Tetramine constitutes an additional example of a selective solvent whichis very efiicient in the process of this invention. This compound is oneof a generic group which may be represented by the general formula Thefirst formula is an open chain compound exemplified by diethylenetriamine (NH2.CH4.NH.C2H4.NH2)- triethylene tetramine(NHQ.CzH4.NH.CiHnNHJJaHtNHz) and tetraethylene pentamine(NHz.G2H4LNH.O2H.NH-G2H4.NH.GZH4.NH,)- Examples of the second genericformula, which are ring compounds, are diethylene diamine CQHZ. NE NEand triethylene triamine NHCtHlNK It will be noted that these compoundsare characterized in that they contain more carbon than nitrogen atomsin their molecules and can be formed by the interaction of ethylenedichloride with ammonia followed by liberation of free amine bytreatment with caustic. These compounds which have a boiling point above800 F. are in general eminently suited for use as selective solvents inthe process of this invention.

Although a number of specific examples of suitable selective solventshave been given and although triethylene glycol is at present thepreferred solvent for the process of this invention, it should beapparent to those skilled in the art that the broader aspects of theinvention include the use of a multitude of other selective solvents.High boiling hydroxy ethers, illustrated by diethylene glycol,triethylene glycol and tetraethylene glycol, comprise one chemical typeof selective solvent most suitable for the process herein disclosed.High boiling hydroxy esters, illustrated by diacetin, dibutyl tartrate,and butyl lactate, are also suitable. Carbitol acetate and butylCarbitol illustrate operative compounds containing hydroxy, ether andester groups.

Experiments indicate that polar compounds selected from the groupconsisting of hydroxy benzenes, amines, amides, chlorinatedhydrocarbons, esters of polycarboxylic acids, and phosphoric acid estersof hydroxy benzenes are in general operative in the process of thisinvention. As previously pointed out the solvent selected from thisgroup should have a boiling point sufiiciently high so that it can bereadily maintained in liquid phase under the conditions of extraction.In general, a boiling point above approximately 300 F. is desirable.

This application is a division of our copending application Serial No.159,522, filed August 17, 1937, and issued as Patent No. 2,215,915,dated Sept 24, 1940.

While the character of this invention has been described in detail andnumerous illustrative examples given, this has been done by way ofillustration only and with the intention that no limitation should beimposed upon the invention thereby. It will be apparent to those skilledin the art that numerous modifications and variations may be effected inthe practice of this invention which is of the scope of the claimsappended hereto.

We claim:

1. A process of separating components of a. complex mixture containingaromatic and non-aromatic carbon compounds having overlapping boilingranges which comprises passing said mixture through an extraction zone,passing a liquid phase selective solvent through said extraction zone,intimately contacting said mixture with said liquid phase selectivesolvent, maintaining said selective solvent in said zone at atemperature no lower than the boiling point of said mixture, separatinga vapor phase non-aromatic raflinate from said liquid phase solvent,removing the liquid phase solvent containing dissolved aromatichydrocarbons from said extraction zone, passing said solvent togetherwith its dissolver compounds to a separate stripping zone, maintaininga. seal between said solvent extraction and stripping zones to preventundesired return of vaporized compounds, and altering the conditions insaid extraction zone by returning to said zone controlled amounts ofvapor phase hydrocarbons stripped from said solvent phase in saidstripping zone, said controlled amounts consisting of only the morereadily vaporized portion of the hydrocarbons dissolved in saidselective solvent.

2. A process of separating components of a complex mixture containingaromatic and nonaromatic carbon compounds having overlapping boilingranges which comprises passing said mixture through an extraction zone,passing a liquid phase selective solvent through said extraction zone,intimately contacting said mixture with said liquid phase selectivesolvent, maintaining said selective solvent in said zone at atemperature no lower than the boiling point of said mixture, separatinga vapor phase non-aromatic ramnate from said liquid phase solvent,partially condensing said vapor phase raifinate, returning said partialcondensate to said extraction zone, removing the liquid phase solventcontaining dissolved aromatic hydrocarbons from said extraction zone,passing said solvent together with its dissolved compounds to a separatestripping zone, maintaining a seal between said solvent extraction andstripping zones to prevent undesired return of vaporized compounds, andaltering the conditions in said extraction zone by returning to saidzone controlled amounts of vapor phase hydrocarbons stripped from saidsolvent phase in said stripping zone, said controlled amounts consistingof only the more readily vaporized portion of the hydrocarbons dissolvedin said selective solvent.

3. A process of separating components of a complex mixture containingaromatic and nonaromatic carbon compounds having overlapping boilingranges which comprises passing said mixture through an extraction zone,passing a liquid phase selective solvent through said extraction zonecountercurrently to said mixture and in an amount of from approximatelythree parts solvent to one part mixture to approximately five partssolvent to one part mixture, intimately contacting said mixture withsaid liquid phase selective solvent, maintaining said selective solventin said zone at a temperature no lower than the boiling point of saidmixture, separating a vapor phase non-aromatic raflinate from saidliquid phase solvent, removing the liquid phase solvent containingdissolved aromatic hydrocarbons from said extraction zone, passing saidsolvent together with its dissolved compounds to a separate strippingzone, maintaining a seal between said solvent extraction and strippingzones to prevent undesired return of vaporized compounds, and alteringthe conditions in said extraction zone by returning to said zonecontrolled amounts of vapor phase hydrocarbons stripped from saidsolvent phase in said stripping zone, said controlled amounts consistingof only the more readily vaporized portion of the hydrocarbons dissolvedin said selective solvent.

4. A process of separating a petroleum fraction into four fractions ofdistinctly different chemical constitution which comprises passing saidpetroleum fraction through a series of at least three extraction zones,passing a liquid phase selective solvent through each of said extractionzones, intimately contacting the petroleum and the selective solvent insaid zones, maintaining said selective solvent in each of the zones at atemperature no lower than the boiling point of the petroleum fractionunder the conditions of extraction in that zone, maintaining thetempera,-

ture of the solvent above the boiling point of the non-aromaticcompounds in the first zone of extraction but below the point at whichall aromatic compounds would be vaporized from the solvent, maintainingthe temperature of the solvent in the second extraction zone above theboiling point of paraffinic and naphthenic compounds but below the pointat which all sulfur bodies would be vaporized from the selectivesolvent, maintaining the temperature of the solvent in the thirdextraction zone above the boiling point of paraffinic compounds butwithin the range at which substantially all the cyclic non-benzenoidcompounds are selectively dissolved, removing paraffinic compounds invapor phase from said third extraction zone, removing cyclicnon-benzenoid compounds in the extract phase of said third zone,removing sulfur bodies in the extract phase from said second zone, andremoving aromatic compounds in the extract phase of said first zone.

5. A process of separating components of a complex mixture containingaromatic and nonaromatic carbon compounds having overlapping boilingranges which comprises passing a liquid phase selective solvent in onedirection through a series of extraction zones, introducing said complexmixture into an intermediate one of said zones, intimately contactingsaid mixture and selective solvent in said zone, maintaining theselective solvent at a temperature no lower than the boiling point ofsaid mixture in said zone, separating a vapor phase raffinate from saidliquid phase selective solvent, passing said vapor phase rafiinateccuntercurrently to said selective solvent in the remaining extractionzones on one side of the aforesaid intermediate zone, removing theliquid phase solvent containing dissolved aromatic compounds from saidintermediate extraction zone, passing said solvent through the remainingextraction zones on the other side of said intermediate zone,introducing an additional portion of said complex mixture into theaforesaid remaining extraction zones, and countercurrently contactingsaid liquid phase solvent with said additional portion of the mixture.

6. A process of separating components of a complex mixture containingaromatic and non-aromatic hydrocarbon compounds having overlappingboiling ranges which comprises passing said mixture through anextraction zone, passing a liquid phase selective solvent through saidextraction zone, intimately contacting said mixture with said liquidphase selective solvent, maintaining said selective solvent in said zoneat a temperature no lower than the boiling point of said mixture,separating a vapor phase non-aromatic railinate from said liquid phasesolvent, removing the liquid phase solvent containing dissolved aromatichydrocarbons from said extraction zone, passing said solvent togetherwith its dissolved compounds to a separate vaporizing zone, maintaininga seal between said solvent extraction and vaporizing zones to preventundesired return of vaporized compounds, vaporizing only a portion ofthe hydrocarbons dissolved in said solvent in said vaporizing zone, andreturning said vaporized hydrocarbons to said solvent extraction zone.

'7. A process of treating a petroleum fraction with a selective solventwhich comprises passing a petroleum fraction containing aromatic, cyclicnon-benzenoid, and paraffinic compounds through a series of extractionzones, passing resorcinol through each of said extraction zones at atemperature substantially below its boiling point, intimately contactingthe petroleum and the resorcinol in said zones, maintaining theresorcinol at a temperature no lower than the boiling point of thepetroleum fraction under the conditions of extraction, maintaining thetemperature of said resorcinol above the boiling point of thenon-aromatic compounds in the first zone of extraction and selectivelydissolving aromatics in said resorcinol, maintaining the temperature ofsaid resorcinol in a second extracting zone above the boiling point ofthe paraihnic compounds and selectively dissolving cyclic non-benzenoidcompounds in the resorcinol, and removing paraffmic compounds in vaporphase from the last of said extraction zones.

8. A process of treating a petroleum fraction with a selective solventwhich comprises passing a petroleum fraction containing aromatic, cyclicnon-benzenoid, and parafiinic compounds through a series of extractionzones, passing diacetin through each of said extraction zones at atemperature substantially below its boiling point, intimately contactingthe petroleum and the diacetin in said zones, maintaining the diacetinat a temperature no lower than the boiling point of the petroleumfraction under the conditions of extraction, maintaining the temperatureof said diacetin above the boiling point of the nonaromatic compounds inthe first zone of extraction and selectively dissolving aromatics insaid diacetin, maintaining the temperature of said diacetin in a secondextracting zone above the boiling point of the paraffiric compounds andselectively dissolving cyclic non-benzenoid compounds in the diacetin,and removing parafiinic compounds in vapor phase from the last of saidextraction zones.

9. A process of treating a petroleum fraction with a selective solventwhich comprises passing a petroleum fraction containing aromatic, cyclicnon-benzenoid, and paraffinic compounds through a series of extractionzones, passing anisidine through each of said extraction zones at atemperature substantially below its boiling point, intimately contactingthe petroleum and the anisidine in said zones, maintaining the anisidineat a temperature no lower than the boiling point of the petroleumfraction under the conditions of extraction, maintaining the temperatureof said anisidine above the boiling point of the non-aromatic compoundsin the first zone of extraction and selectively dissolving aromatics insaid anisidine, maintaining the temperature of said anisidine in asecond extracting zone above the boiling point of the paraflmiccompounds and selectively dissolving cyclic non-benzenoid compounds inthe anisidine, and removing paraifinio compounds in vapor phase from thelast of said extraction zones.

JOHN Q. COPE. WILLIAM H. CLAUSSEN.

